The WhenToTest site is focused on an organizational response to COVID-19 by schools and businesses. For basic information on the disease and how individuals can mitigate the spread, the following resources provide excellent information:

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1. COVID-19 TESTING: THE BASICS

  • How do COVID-19 variants affect testing?

     

    The CDC and FDA, in partnership with the major testing laboratories, continue to carefully monitor the emergence of variants and how their genetic characteristics might affect testing.

    NOTE: As part of its calculations, the When to Test Calculator includes a default measurement of how transmissible the virus is. That measurement is called R0 (“R-naught”) or the basic reproduction number for the virus. WhentoTest.org follows CDC guidance to set the Calculator’s default for R0 under typical conditions. The R0 for hotspot conditions is an estimate of the R0 for the Delta variant. If you would like to set a specific R0 in your scenarios, you can do so under Advanced Settings: Main Calculator Settings.

    CDC COVID-19 Pandemic Planning Scenarios

    FDA Issues Alert Regarding SARS-CoV-2 Viral Mutation

  • What's the difference between a Rapid Antigen Test and Antigen w/ Instrument in the Calculator?

     

     

    Both Rapid Antigen tests and Antigen w/ Instrument tests are point-of-care COVID-19 tests that look for viral proteins and return results within minutes. For the purposes of the When to Test Calculator, the differences between these two types are as follows:

    Rapid Antigen Test

    • Uses paper-based lateral flow technology
    • Looks like a pregnancy test
    • Once the test is used, it is discarded
    • Some of these tests can be completed by the person being tested; others require trained staff to obtain samples and/or run the test itself
    • Has a lower sensitivity than Antigen w/ Instrument (see note below)

    Antigen w/ Instrument

    • Requires a small piece of equipment to run the test
    • The instrument must be purchased separately from test kits and maintained over time
    • Your organization may need to purchase several instruments in order to be able to test your population quickly enough
    • Requires trained staff to run the tests and maintain the instrument(s)
    • Has a higher sensitivity than Rapid Antigen (see note below)

    IMPORTANT NOTE: The sensitivity and specificity of both rapid antigen tests and antigen with instrument tests vary a great deal between test brands. If your organization decides to use one of these test types either for asymptomatic screening or for follow-up for pooled testing, check the sensitivity and specificity of the brand of test you plan to use. Then go to Advanced Settings in the When to Test Calculator, click on the tab for the relevant test type, and adjust the sensitivity and specificity settings to match your brand of test.

  • What is follow-up testing, and how does it work?

     

    Follow-up testing is a critical part of pooled testing. In pooled testing, samples are gathered from multiple people and mixed together into a pool. Instead of testing each individual sample on its own, the lab tests the pool. If a pool tests positive, then at least one individual in the pool may be positive for COVID-19. When this happens, follow-up testing, sometimes referred to as “reflex testing” or “deconvolution,” is required. If follow-up testing isn’t possible, then the entire pool should isolate.

    In follow-up testing, each person or each sample in the positive pool is individually retested to determine which individual(s) in the positive pool are infected. The way follow-up testing happens depends in part on how and where the samples are pooled.

    The When to Test Calculator identifies four testing strategies for follow-up testing a positive pool. Details on each strategy appear beneath the table below.

    Automatic

    Pooling Process: Individual samples are collected on-site and taken to an off-site lab. The lab creates the pools and tests the pooled samples using PCR.

    Follow-Up Testing Process: When a positive pool is identified, the lab automatically retests the individual samples that went into the pool using PCR.

    Pros and Cons

    • Eliminates need to re-collect individual samples.
    • Results are provided faster than other pooled testing strategies.
    • May be 2-3x more costly per test than rapid antigen and on-site PCR follow-up.

    On-Site Rapid Antigen

    Pooling Process: Individual samples are collected and pooled on-site. The pooled samples are taken to an off-site lab, which tests them using PCR.

    Follow-Up Testing Process: When a positive pool is identified, all individuals in the positive pool must be resampled. Individual follow-up tests are completed on-site, using rapid antigen tests.

    Pros and Cons

    • Faster than off-site PCR follow-up.
    • Likely to be least expensive option.
    • Requires trained staff on site.
    • Slightly less accurate than PCR follow-up.

    On-Site PCR

    Pooling Process: Individual samples are collected and pooled on-site. The pooled samples are taken to an off-site lab, which tests them using PCR.

    Follow-Up Testing Process: When a positive pool is identified, all individuals in the positive pool must be resampled. Individual follow-up tests are completed on-site, using PCR instruments.

    Pros and Cons

    • Faster than off-site PCR follow-up.
    • Less expensive than automatic or off-site PCR follow-up.
    • Requires PCR instruments and trained staff on site.
    • Highly accurate.

    Off-Site PCR

    Pooling Process: Individual samples are collected and pooled on-site. The pooled samples are taken to an off-site lab, which tests them using PCR.

    Follow-Up Testing Process: When a positive pool is identified, all individuals in the positive pool must be resampled. Samples are shipped to an off-site lab, where individual follow-up tests are completed with PCR.

    Pros and Cons

    • Slowest pooling option.
    • More expensive than on-site follow-up.
    • Highly accurate.

    For more information on pooled testing, please download our K-12 Playbook where you can read more about pooling on page 20.

  • What’s the difference between COVID-19 screening (aka asymptomatic screening) and diagnostic testing?

     

    Screening for COVID-19, also referred to as screening testing or asymptomatic screening, means testing your population to identify infected people who are not showing symptoms. Diagnostic testing for COVID-19 is performed when infection is suspected, such as when the person:

    • Has COVID-19 symptoms or
    • Has no symptoms, but has had a recent known or suspected exposure to SARS-CoV-2 (the virus that causes COVID-19).

    Asymptomatic screening is typically a regularly scheduled event (e.g., 1x/week). Along with other COVID-19 mitigation strategies, screening can help prevent outbreaks in your school or workplace.

    Not many tests have authorization from the FDA specifically for screening testing. However, the FDA supports the use of COVID-19 tests that have Emergency Use Authorization (EUA) when used “off-label” under the supervision of a physician or other prescriber.

    NOTE: The When to Test Calculator assumes that tests that do not have FDA authorization for screening are used off-label under practitioner guidance.
     

  • What's the difference between PCR and antigen tests?

     

    PCR tests, also known as molecular tests, look for pieces of the virus’s genetic material using a lab technique called polymerase chain reaction (PCR). They are the most accurate kind of test for COVID-19 currently available.

    PCR samples are usually sent for processing and analysis in a lab, and results can take anywhere from a few hours to several days to arrive. Lab-based PCR tests tend to be more costly than other types of test. However, some point-of-care PCR tests are now available, as well. Most point-of-care PCR tests require trained staff members to run them, and depending on the size of your organization, you may need to purchase multiple instruments on which to run the tests. Point-of-care PCR tests typically return results in under an hour.

    Antigen tests look for viral proteins. These tests typically provide results within minutes and are very good at accurately identifying people who are shedding a lot of virus particles. They are not as good as PCR tests are at finding people who aren't carrying as much virus, including children and asymptomatic adults. Many antigen tests still require trained staff to run them, but a few are now available over the counter. Antigen tests tend to be the least expensive type of test.

    Because of their decreased sensitivity, antigen tests have the following limitations:

    • If your organization uses antigen tests for screening, you may need to test more frequently than you would if you were using a PCR test in order to prevent an outbreak.
    • Positive results on antigen tests whose specificity is >99% are usually correct, but negative results may need to be confirmed with a PCR test.

    Remember, no test is perfect. When you choose a type of test for your organization, be sure to understand how its sensitivity and specificity will affect its performance in the population you’ll be testing (adults vs. children, people with symptoms vs. people without symptoms).

    Coronavirus Disease 2019 Testing Basics

    CDC - Interim Guidance for Rapid Antigen Testing

  • I’m worried that if I test asymptomatic people, I’ll get a lot of false positives and will have to isolate and quarantine people unnecessarily. What do I do?

     

     

    The best way to avoid false positives is to choose a test with high specificity (>99%). A test’s specificity indicates how good it is at designating someone who DOESN’T have the disease as negative. People who test positive using tests with high specificity are very likely to truly have the disease, which means that very few people will be isolated and quarantined unnecessarily.

    If you’re in an area with very low prevalence of disease, it’s especially important to choose a test with high specificity, because the likelihood of false positives becomes higher under those conditions.

  • I'm not familiar with on-site PCR tests. How are they different from antigen tests and in-lab PCR tests?

     

    On-site PCR tests use a small instrument to conduct a polymerase chain reaction (PCR)-based test on a sample. Depending on the size of your organization, you may need to purchase multiple instruments in order to test your population quickly enough to prevent an outbreak.

    On-site PCR tests are not quite as sensitive as in-lab PCR tests, but they are typically more sensitive than antigen tests. These tests return results quickly – typically in under an hour – but are not as fast as rapid antigen tests. They require trained staff to run and maintain them.

  • How can I tell if pooled testing is a good fit for my organization?

     

    Pooled testing, also known as pooling, is a way to provide highly sensitive PCR testing for your organization in a more cost-effective way. In pooled testing, samples are gathered from multiple people and mixed together into a pool. Instead of testing each individual sample on its own, the lab tests the pool, thus using fewer resources and lowering processing costs.

    Pooled testing could be a good fit for your organization if:

    • Positivity rates in your community are relatively low (i.e., you don’t expect a lot of people in your organization to test positive)
    • You want the sensitivity of PCR testing
    • You don’t want to train or pay staff to do testing on-site (however, some types of pooled testing do require on-site follow-up testing)
    • You can’t test more frequently than once a week

    Pooled testing is not a good fit for your organization if:

    • Positivity rates in your community are very high (i.e., you expect a lot of people in your organization to test positive)
    • You need immediate test results

    CDC – Guidance for Use of Pooling Procedures

    FDA – Pooled Sample Testing

    Open and Safe Schools — Includes toolkit on how to start a pooled testing program at your school.

  • There are a lot of different kinds of antigen tests out there. How do I select one for my organization to use?

     

    In addition to the cost of the individual test kits, the following criteria can inform your choice:

    Accuracy: Most antigen tests have a very high specificity. However, the sensitivity of the different brands of tests varies. The When to Test Calculator assumes a lower sensitivity for Antigen tests than with PCR tests, to ensure that the recommended testing frequency is adequate to prevent an outbreak.

    Capital expenditures and maintenance: Some antigen tests run on a small testing instrument, which must be purchased separately and maintained over time. Depending on size of your organization, you may need to purchase several of these instruments in order to be able to test your population quickly enough to prevent an outbreak.

    Staffing requirements: Some antigen tests require trained staff to obtain samples and/or run the tests. If you use an instrument-based antigen test, you will need staff to maintain the instruments, as well. Other types of antigen tests can be performed entirely by the person being tested.

    Time: Some rapid antigen tests can be done at home, decreasing the amount of time taken away from work or school for testing purposes.

    Access: Manufacturing of antigen tests has not always kept up well with demand, so some businesses may find they have a limited selection of brands from which to purchase. Some schools will only have access to a single type of antigen test, which is provided or mandated by the state.

  • What is pooled testing?

     

    Pooled testing, also known as pooling, is a way to make highly sensitive PCR testing more cost-effective. In pooled testing, samples are gathered from multiple people and mixed together into a pool. Instead of testing each individual sample on its own, the lab tests the pool, thus using fewer resources and lowering processing costs.

    If a pool tests negative, then all individuals in that pool are ‘clear’ or negative for COVID-19 and may continue to attend class, work, or other activities.

    If a pool tests positive, then at least one individual in the pool may be positive for COVID-19. When this happens, follow-up testing, sometimes referred to as “reflex testing” or “deconvolution,” is required. Follow-up testing can be done at a central lab or on-site.

    In follow-up testing, each person or each sample in the positive pool is individually retested to determine which individual(s) in the positive pool are infected. If follow-up testing isn’t possible, then the entire pool should isolate. Pooled testing should be done at a lab, using a PCR test that has Emergency Use Authorization (EUA) from the FDA. The lab’s pooling system should either have EUA or be internally validated.

    CDC – Guidance for Use of Pooling Procedures

    FDA – Pooled Sample Testing

    Open and Safe Schools — Includes toolkit on how to start a pooled testing program at your school.

    When To Test K-12 Playbook for COVID-19

  • What is the difference between point of care (POC) testing and lab-based testing?

     

    In point-of-care (POC) testing, all testing steps, including sampling and analysis, take place close to or near the patient. For the When to Test Calculator, this means that testing is completed on-site, at your organization’s location. Point-of-care tests give you results quickly. Most of them are antigen tests, but some point-of-care PCR tests are available, as well.

    In lab-based or off-site testing, samples are gathered on-site at your organization and are sent to a central lab for processing and analysis.Lab-based tests are generally PCR tests, which are highly accurate. However, they take longer to return results than point-of-care tests do. In some cases, the turnaround time of lab-based tests is not fast enough to prevent an outbreak.

    CDC - Guidance for COVID-19 Point-of-Care Testing

  • What kinds of tests can be used for COVID-19 screening or diagnostic testing?

     

    Both kinds of testing can be done using either a PCR (also known as molecular) or antigen test.

    PCR tests look for pieces of the virus’s genetic material. They are the most accurate kind of test for COVID-19 currently available.

    Antigen tests look for viral proteins. They are slightly less accurate than PCR tests.

    Antibody tests (also known as serology tests) look for antibodies to SARS-CoV-2 (the virus that causes COVID-19). Those antibodies can come from a past COVID-19 infection or from a COVID-19 vaccine. This kind of test cannot be used to diagnose an active COVID-19 infection.

    CDC - Interim Guidance for Rapid Antigen Testing

  • What is confirmatory testing, and why would my organization need it?

     

    Confirmatory testing is done to make sure the results of a test are correct. In most cases, confirmatory testing is used to verify whether a negative result on a COVID-19 antigen test is accurate.

    If a test with a specificity of less than 99% comes back positive, especially in low-prevalence environments, confirmatory testing is also recommended. Asymptomatic screening programs are frequently supplemented by confirmatory testing because false positives are more common when screening asymptomatic individuals.

    CDC - Interim Guidance for Rapid Antigen Testing

  • What is an antibody test? Can it be used to diagnose a COVID-19 infection?

    Antibodies are proteins created by your immune system to help you fight off infectious microbes. Your body makes them after you’ve been infected or vaccinated.

    Antibody tests (also known as serology tests) look for antibodies to SARS-CoV-2 (the virus that causes COVID-19). They cannot be used to diagnose an active COVID-19 infection, because it can take up to three weeks after the infection for your immune system to make antibodies. These tests can only be used to determine whether someone had COVID-19 or a COVID-19 vaccine in the past.

  • What are sensitivity and specificity?

     

    Sensitivity refers to how well a test designates someone who HAS the disease as positive.

    If you have a test with 95% sensitivity and you test 100 people who have COVID-19, 95 will test positive (true positive) and 5 will test negative (false negative). Tests with high sensitivity will find most cases of the virus. They will return few false negatives.

    Specificity is how well a test designates someone who DOESN’T have the disease as negative.

    If you have a test with 95% specificity and you test 100 people without COVID-19, 95 will test negative (true negative) and 5 will test positive (false positive). People who test positive using tests with high specificity are very likely to truly have the disease. These tests return few false positives.

    In an ideal world, all tests would be both highly sensitive and highly specific. Unfortunately, that’s not possible most of the time. It’s also important to acknowledge that no test is perfect - no test will have 100% sensitivity and specificity.

  • What does Emergency Use Authorization (EUA) mean?

     

    In the US, the use of medical tests is regulated by the Food and Drug Administration (FDA). Under normal circumstances, these tests can only be used in this country once they’ve undergone a months-long approval process. In early 2020, the US was in desperate need of tests for COVID-19; we couldn’t wait months for tests to arrive. For this reason, the US Secretary of Health and Human Services declared that the FDA could use Emergency Use Authorization to make COVID-19 tests available more quickly.

    As its name suggests, EUA is a seldom-used type of authorization which is only allowed during public-health emergencies. It enables the FDA to authorize the use of medical products (including tests) that haven’t undergone the long approval process, provided that “certain criteria are met.” At a minimum, the product must have known and potential benefits that outweigh its known potential risks. In addition, there must be “no adequate, approved, and available alternatives” to the product receiving the EUA.

    There are currently no COVID-19 tests that have complete approval from the FDA. Those that have EUA have undergone a shortened version of the approval process, which ensures that they meet the criteria mentioned above, among other requirements. The When to Test Calculator assumes that your organization is using a test that has received EUA.

    FDA – Emergency Use Authorization
     

2. COVID-19 MITIGATION STRATEGIES

  • How does mask wearing impact my organization's need for testing?

     

    The more people in your organization who wear masks consistently and properly, the less testing you will need to do to prevent an outbreak. Remember: a well-fitted mask, worn properly, covers both the nose and the mouth and does not leave gaps.

    The When to Test Calculator asks you to estimate what percentage of people in your organization wear their masks properly at all times when indoors. Most people tend to overestimate the percentage of people in their own organizations who do this, so you may want to input a number a bit lower than you were first considering.

    In most organizations, people wear a variety of different kinds of masks. The When to Test Calculator takes that fact into consideration in its default assumptions about how well masks work. If your organization mandates the use of N95s or other high-efficiency masks for all employees, you can change the Calculator’s defaults under Advanced Settings: Main Calculator Settings.

    CDC - Use Masks to Slow the Spread of COVID-19
     

  • How does limiting unmasked high-COVID-risk activities indoors affect my organization's testing needs? How does cohorting factor into this mitigation strategy?

     

     

    Limiting the size of groups who participate in unmasked high-COVID-risk activities indoors is an extremely effective way to reduce COVID-19 transmission risk, and thus reduce your organization’s need for testing.

    With increasing levels of vaccination in the US, many organizations have decided to do away with mask-wearing altogether. However, even if your organization no longer has a mask policy, some activities remain higher risk than others in terms of their potential for COVID transmission. Any activity that brings a group of people together in close proximity for an extended period of time – most commonly, eating and/or drinking together at the same table – is a high-COVID-risk activity. Other high-COVID-risk activities are those that involve breathing heavily and/or with force, such as sports activities, singing, and playing wind instruments, whether or not the participants are in close proximity to one another.

    If your organization permits any high-COVID-risk activities indoors, then the number you would input in this section of the Calculator is the largest group that participates in such activities together. For example, if you have a choir of 10 people and a basketball team of 25, you would input “25.” Doing so allows the Calculator to factor in the additional layer of risk added by permitting these kinds of activities to happen indoors. ** Calculator summary: "Properly Masked" = 0%; "Unmasked Cohort Size" = size of largest group that participates in high-COVID-risk activities together.

    Organizations that DO require masks indoors

    If your organization maintains a mask policy, then ideally, no unmasked group activities would occur indoors at your facility. If this is the case, then the number you would input as "Unmasked Cohort Size" should be zero ("0"). If individuals are allowed to eat or drink or work out unmasked in the onsite gym alone, then the number you input should be one ("1"). ** Calculator summary: "Properly Masked" = your estimate for your organization; "Unmasked Cohort Size" = zero ("0") or one ("1").

    If your organization does allow unmasked indoor group activities, you can still mitigate risk by dividing your population into cohorts and ensuring that each individual is only allowed to participate in unmasked indoor activities with members of their own cohort. If your organization does this, then the number you input in this section of the Calculator should be the size of your organization’s largest cohort.

    ** Calculator summary: "Properly Masked" = your estimate for your organization; "Unmasked Cohort Size" = size of largest group that participates in unmasked indoor high-COVID-risk activities together.

    Some organizations divide their populations into cohorts for unmasked indoor activities, but then allow members of the cohorts to overlap. As an example, consider a workplace whose cafeteria has 20 tables that are well distanced from one another, and each table seats a cohort of eight people. If individuals are permitted to eat lunch with different people on different days, then those cohorts overlap. A school that allows some students to both sing in choir and then also play on the basketball team would be in the same situation: It has overlapping unmasked indoor cohorts.

    Because of the way the Calculator weights the various inputs, allowing unmasked indoor cohorts to overlap has the same effect as eliminating your organization’s masking policy. For that reason, if your organization has overlapping cohorts, you should enter zero (“0”) under the “Properly Masked” input. You would then enter the size of your largest cohort under the “Unmasked Cohort Size” input. ** Calculator summary: "Properly Masked" = 0%; "Unmasked Cohort Size" = size of largest group that participates in unmasked indoor high-COVID-risk activities together.

    NOTE: The Calculator assumes that cohorts of people eating or drinking together are physically distanced from other people in the room. Thus, if your cafeteria has 20 tables that each seat a cohort of eight people and the tables are more than six feet apart, the size of the cohort is eight.

    However, physical distancing has its limits. If people in your organization are participating in unmasked indoor group activities that involve significant exertion or air expulsion (for example, sports, gym classes, or singing), then the cohort size should be the total number of people in the room, regardless of their distance from one another.

    CDC - Resource on Cohorts in a K-12 school

    Oregon Department of Education —  One example of a school-based cohorting system.

  • How does my organization's ability to identify and notify close contacts affect our testing needs?

     

    The faster your organization can identify and notify close contacts of an infected person, the lower your need for testing will be. The reason for this has to do with how contact tracing works and how it affects the likelihood of an outbreak.

    The goal of contact tracing is to identify the people who were in close contact with an infected person while they were contagious, so that those people can be prevented from spreading the disease to others. The faster close contacts are identified and notified of their status, the sooner they can quarantine, and the less likely it is that they will infect other people.

    For COVID-19, the definition of a close contact is someone who was within six feet of an infected person while they were contagious, for a total of at least 15 minutes over the course of 24 hours. When someone with no symptoms tests positive for COVID-19, it’s assumed that they were contagious for the 48 hours (two days) before they provided the sample that was tested.

    In practice, identifying exactly who has been in “close contact” with someone over the course of two days can be quite difficult unless your organization keeps good records. Schools often keep seating charts for classrooms, school buses, and lunch tables for this purpose. In addition, teachers may keep track of which students tend to walk next to one another in the hallways. In an office setting, keeping records of in-person meeting attendance and assembly-line stations may be helpful.

    NOTE: The When to Test Calculator assumes that only 50% of an infected person’s close contacts are identified and notified of their status within 24 hours (a contact-tracing efficiency of 0.5). This assumption may be changed in the Calculator’s defaults under Advanced Settings: Main Calculator Settings.

    CDC - Close Contact definition

    CDC - Contact Tracing for COVID-19

    CDC – What you can expect to happen during contact tracing

  • Can my organization require that our population (i.e., employees and/or students) be vaccinated?

     

     

    For information about this and other questions about COVID-19 regulations in the workplace, please check the US Equal Employment Opportunity Commission’s (EEOC) website, listed below.

    Vaccination requirements for students are typically set at the state level. Please contact your state department of education for further guidance.

    EEOC – Coronavirus and COVID-19

    US Department of Education – State Contacts
     

  • Can my organization ask members of our population (i.e., employees and/or students) whether they have been vaccinated?

     

    Yes, but people may choose on an individual basis to decline to answer the question. Once an employer has information about an individual’s vaccine status, they must keep it confidential and separate from the rest of the employee’s personnel files, per the Americans with Disabilities Act (ADA).

    US Department of Health and Human Services – The HIPAA Privacy Rule

    EEOC – Coronavirus and COVID-19

  • How does vaccination impact my organization's need for testing? Do vaccinated people still need to be tested?

     

    The more people in your organization who are vaccinated, the less testing you will need to do to prevent an outbreak. If you aren’t sure what percentage of your organization has been fully vaccinated, you can use published estimates for your area, available via the links below.

    While the CDC recommends that fully vaccinated people “refrain from routine screening testing if feasible,” participation in screening testing is contractually required in some workplaces. Thus, the When to Test Calculator assumes that vaccinated individuals in your organization will continue to participate in screening. If you plan to test only the unvaccinated members of your organization, then you should model them as a separate group.

    CDC – Interim Public Health Recommendations for Fully Vaccinated People

    CDC – COVID-19 Integrated County View — Does not include Texas, Hawaii, and some counties in California and Alaska.

    CDC – COVID-19 Vaccinations in the United States — State-by-state vaccination statistics.
     

3. USING THE WHEN TO TEST CALCULATOR

  • When should I use Hotspot conditions?

     

     

    The answer to this question depends on whether your organization has already done baseline COVID-19 testing of your population. Baseline testing means that you’ve tested 100% of your population before starting a regular COVID-19 testing program. Doing baseline testing will help you get the most accurate results from the When to Test Calculator.

    If your organization has already done baseline testing

    If less than 1% of your population was positive on baseline testing, then use TYPICAL conditions. Otherwise, use HOTSPOT conditions.

    If your organization has not done baseline testing

    If baseline testing has not been performed, use publlished information about the COVID-19 status of your community as a guide. If Delta is the most common variant in your area, use HOTSPOT conditions. If you're not sure which variant is most common in your community, check your area's published test positivity rates. If those rates are greater than 1%, use HOTSPOT conditions.

  • How do I know if I need to test at all? When can I stop testing?

     

    If your conditions are favorable and your organization has excellent mitigation measures in place, you may not need to regularly test people without COVID-19 symptoms in order to effectively reduce the chance of an outbreak. In those cases, the Calculator will recommend “Symptomatic Screening Only,” meaning that you should continue to require COVID-19 testing for people who display symptoms, but you do not need to test those who are symptom-free.

    To reach this goal, consider how your organization might improve mitigation measures other than testing, such as by emphasizing consistent mask-wearing, incentivizing vaccination among employees, keeping better track of close contacts, or decreasing the size of cohorts that participate in unmasked activity together. Use the Calculator to model various scenarios and predict how improvements in these areas can change your test recommendations.

    Once you’ve modeled a scenario that you believe is achievable, take steps to make those improvements a reality within your environment.

    NOTE: The Calculator’s results for typical conditions are based upon the CDC’s guidance of R0, and upon the assumption that your organization has already performed baseline testing (testing 100% of all of its members prior to beginning an asymptomatic screening program). It’s a good idea to be prepared to institute asymptomatic screening should your organization’s situation change, and to frequently recheck the Calculator’s results for your organization.

  • "Symptomatic Screening Only" appeared in the Frequency column of my calculator results table. What does that mean?

     

     

     

    The When to Test Calculator tells you how often your organization needs to perform what is called “asymptomatic screening,” or testing people who do not have COVID-19 symptoms. The goal of asymptomatic screening is to find and isolate infected people who do not have symptoms, in order to prevent them from transmitting the virus to others.

    If your conditions are favorable and your organization has excellent mitigation measures in place, you may not need to do asymptomatic screening in order to effectively reduce the chance of an outbreak. In those cases, the Calculator will recommend “Symptomatic Screening Only,” meaning that you should continue to require COVID-19 testing for people who display symptoms, but you do not need to test those who are symptom-free.

    NOTE: The Calculator’s results are based upon the CDC’s most recent guidance regarding how transmissible the most common variants of the virus are. It’s a good idea to be prepared to institute asymptomatic screening should your organization’s situation change, and to frequently recheck the Calculator’s results for your organization.
     

  • Why does the Calculator recommend that we test more frequently if we're using antigen tests rather than PCR?

     

     

    In general, antigen tests are less sensitive than PCR tests. That means they are not as good as PCR tests are at finding people who aren't carrying as much virus, including children and asymptomatic adults. Testing more frequently helps to make up for the antigen tests’ lower sensitivity.

    In addition, people who were infected very recently often carry low levels of virus, so if you test them using an antigen test at that time, they may test negative. A few days later, when their virus levels have risen significantly, an antigen test will come back positive. Because PCR is more sensitive, it can catch an infection early in the disease course, eliminating the need for another test.

  • What are the main differences between the various test types listed in the calculator results?

     

    The amount of testing your organization needs to do depends in part on the type of test you use. The When to Test Calculator returns results for the test categories listed in the table below, as well as additional results for other pooled testing strategies.

    NOTE: The test categories shown in the When to Test Calculator are examples only; they do not represent any one individual test.

    For more information, see the following FAQ topics:

  • Why does the When to Test Calculator show me two sets of results?

     

    The Calculator is designed so that you can compare how your organization’s testing needs would change if you altered your mitigation strategies. It can also allow you to compare the testing needs of different cohorts of people within your organization.

  • Under the Implementation Details tab, what does "Recommended max days between tests/person" mean?

     

    Some people in your organization may not be on-site every day. Those people still need to be tested on essentially the same schedule as those who are onsite on a daily basis.

    For example, if the When to Test Calculator lists the recommended max days between tests/person as “7,” then all individuals in your organization should be tested once every seven calendar days, regardless of how frequently they come to your site.

    This calculation assumes that testing is uniformly spread across the testing period for onsite testing. If it is desired to complete all testing within a shorter period of time, then it may be necessary to hire more staff to conduct sampling and testing and to purchase additional instruments (if an instrument-based test is chosen).

  • I want to compare two different groups of people within my organization. How do I do that?

     

    If your organization includes groups of people whose mitigation strategies are distinctly different (for example, teachers vs. students, office workers vs. assembly-line workers), the When to Test Calculator can show you how those groups’ testing needs differ.

    Here’s an example of how to compare these two groups. The table on the bottom right of the screenshot below shows the Calculator’s results for the teachers in a school. There are 150 teachers (orange arrow), and 75% of them are fully vaccinated (green arrow). This scenario is named TEACHERS (blue arrows).

    Now we want to see the results for the students in this school, who have the same mitigation strategies in place except that only 25% of them are vaccinated. We enter the number of students in the school, and we change the Fully Vaccinated number to 25% (green arrows). That changes the results in the table on the bottom right and brings up the Name New Scenario box (blue arrow). We name this scenario STUDENTS, and save it by clicking Save As (orange arrow).When we click Save As, the new scenario has been named STUDENTS (blue arrows).

    Now we want to compare TEACHERS and STUDENTS side by side. To do that, we go to the drop-down menu above the table on the bottom left and choose TEACHERS (green arrow).Now we see the results for TEACHERS on the bottom left (green arrow) and STUDENTS on the bottom right (blue arrow).

     

  • My organization is a store, restaurant, doctor’s office, or other facility that serves clients in person. Can I use the When to Test Calculator to evaluate my testing needs?

     

    Yes: You can use the Calculator to evaluate the testing needs of your staff. When you input the size of your organization, do not include your clients or other visitors, only the members of your organization.

4. THE WHEN TO TEST CALCULATOR: ADVANCED SETTINGS

  • What is R0 (R-naught)?

     

    R0 (R-naught) is a measure of the average number of people who will contract a contagious disease from one infected person. It’s a measure of viral transmissibility, or how fast the disease is spreading.

    When R0 is exactly 1.0, it means that, on average, one infected person will infect one other person. When R0 is less than 1.0, it means that the spread of the disease is decreasing within the community. When R0 is above 1.0, the spread of disease is increasing.

    The more transmissible a disease or disease variant is, the higher its R0. The When to Test Calculator bases its default R0 for typical conditions on CDC guidance regarding the transmissibility of COVID-19 in the US, as per the CDC - Pandemic Planning Scenarios - Parameter Values. The CDC currently references an R0 of 2.5, based on the original or wild type of SARS-CoV-2, the virus that causes COVID-19.

     

    New variants may have a potentially higher R0. For example, evidence indicates that Alpha (aka B.1.1.7, first identified in the UK) has an R0 approximately 50% higher than the wild type, and Delta (aka B.1.617.2, first identified in India) has an R0 approximately 50 - 60% higher than Alpha. The default R0 for hotspot conditions in the When to Test Calculator is 5.0, which is a low-end estimate of the R0 for the Delta variant.

    If you know which variant is most common in your area and wish to change the R0 in your scenarios to reflect that variant, click on "Show Advanced Settings," then "Main Calculator Settings,” and scroll down to "Estimated R0."

    CDC - US COVID-19 Cases Caused by Variants

  • What is prevalence?

     

    For the purposes of the When to Test Calculator, prevalence is the percentage of individuals in a population who are infected with COVID-19 at any given moment. If you have 100 people in your building and one person has COVID-19, then the prevalence of COVID-19 in your building is 1%.

    The Calculator’s prevalence default settings are 1% for typical conditions and 3% for hotspot conditions.

  • How does the Calculator work?

     

    The model behind the When to Test Calculator was developed as a collaboration by the MIT Institute for Data Systems and Society (IDSS) and the Consortia for Improving Medicine with Innovation & Technology at MGH (CIMIT). This short video explains how it was developed and the science behind it.

5. IMPLEMENTING A TESTING PROGRAM

  • My organization is being provided with tests (or is already using tests) that, based on the Calculator’s results, are insufficient for our needs. What should I do?

     

    If the Calculator’s recommendations for your test type aren’t feasible for your organization, or if they indicate that you cannot prevent an outbreak using that type of test, consider how your organization might improve mitigation strategies other than testing.

    By emphasizing consistent mask-wearing, incentivizing vaccination among employees, keeping better track of close contacts, or decreasing the size of cohorts that participate in unmasked activity together, you can decrease your organization’s reliance on testing as a mitigation measure. Use the Calculator to model various scenarios and predict how improvements in these areas can change your test recommendations.

  • How can my organization improve our ability to identify and notify close contacts?

     

     

    For COVID-19, the definition of a close contact is someone who was within six feet of an infected person while they were contagious, for a total of at least 15 minutes over the course of 24 hours. When someone with no symptoms tests positive for COVID-19, it’s assumed that they were contagious for the 48 hours (two days) before they provided the sample that was tested.

    In practice, identifying exactly who has been in “close contact” with someone over the course of two days can be quite difficult unless your organization keeps good records. Schools often keep seating charts for classrooms, school buses, and lunch tables for this purpose. In addition, teachers may keep track of which students tend to walk next to one another in the hallways. In an office setting, keeping records of in-person meeting attendance and assembly-line stations may be helpful.

    NOTE: The When to Test Calculator assumes that only 50% of an infected person’s close contacts are identified and notified of their status within 24 hours (a contact-tracing efficiency of 0.5).

    CDC - Contact Tracing for COVID-19

    CDC – What you can expect to happen during contact tracing

  • My organization is implementing a testing program. What do we do when someone tests positive?

     

    When an individual in your testing program receives a positive result:

    • Isolate the individual as soon as possible.
    • Review test specificity, and if necessary, perform a confirmatory test.
    • If the person is a minor, contact their family or guardian.
    • Notify your local health department.
    • Notify the doctor or nurse practitioner who provided the standing order for your tests.
    • Initiate contact tracing and request that close contacts quarantine.

    When a pooled test sample comes back positive, all individuals in the positive pool should be isolated until follow-up testing can be performed. Once individual follow-up test results have identified the COVID-19 positive individual(s) in the pool, follow the protocol listed above.

  • My organization is being provided with tests or has already implemented a testing program. How can I apply what I learn from the calculator to this situation?

     

     

    First, figure out what kind of test you are or will be using. (If you’re using pooled testing, you’ll also need to check what kind of follow-up testing you are or will be doing.)

    You can find the list of test types for which the Calculator provides results under the FAQ topic “What are the main differences between the various test types listed in the calculator results?” If you’re not sure which type of test you are or will be using, check with your test vendor for confirmation.

    Once you know your organization’s type of test, look at your results in the Calculator and find the row that matches your test type. (If you’re using pooled testing, you may need to click on “View More Pooling Options” to find the type of follow-up testing your program is or will be using.) The results on that row are the Calculator’s recommended test frequency for your organization.

    If the Calculator’s recommendations for your test type aren’t feasible for your organization, or if they indicate that you cannot prevent an outbreak using that type of test consider how your organization might improve mitigation measures other than testing. By emphasizing consistent mask-wearing, incentivizing vaccination among employees, keeping better track of close contacts, or decreasing the size of cohorts that participate in unmasked activity together, you can decrease your organization’s reliance on testing as a mitigation measure. Use the Calculator to model various scenarios and predict how improvements in these areas can change your test recommendations.

  • The test my organization wants to use for our testing program isn’t authorized for use on people without symptoms. What do I do?

     

     

    Most of the COVID-19 tests on the market that have Emergency Use Authorization (EUA) from the FDA have received that authorization for diagnostic testing: testing individuals who have COVID-19 symptoms. Not many tests have EUA specifically for screening: testing people who don’t have symptoms of COVID-19.

    However, as long as the tests are used under the supervision of a physician or other prescriber, the FDA supports doing off-label screening testing with COVID-19 tests that only have EUA for diagnostic testing.

    NOTE: The When to Test Calculator assumes that tests that do not have FDA authorization for screening are used off-label under practitioner guidance.
     

  • Where can I purchase the kind of test the Calculator recommends for my organization?

     

     

    Visit our collaborator, Project N95, to find a number of COVID-19 tests available for purchase.

    Connect to Test — Created by Arizona State University, this site allows users to input a series of criteria and receive a list of companies and test kits that meet those needs.

    School COVID-19 Testing Partner List — Open and Safe Schools, created by the Shah Family Foundation in partnership with the CDC, provides a list of test vendors that are prepared to work with schools and early education centers. The list is searchable by state and by type of test offered.
     

  • How should my organization go about implementing a testing program?

     

    In the Workplace

    The COVID-19 Testing Implementation Guide — This guide provides practical guidance on the implementation of a COVID-19 testing program, including consideration of various supply, personnel, facilities, and documentation best practices.

    In K-12 Schools and Early Education Centers 

    The COVID-19 Testing Implementation Guide 

    Open and Safe Schools — This website, created by the Shah Family Foundation in partnership with the CDC, provides schools and early education centers with the tools to create a comprehensive COVID-19 testing program. It also includes a list of vendors as well as a database of contacts at schools willing to share their experiences with COVID-19 testing.

    Chiefs for Change Project Planning Workbook — This downloadable Excel spreadsheet, created by the educational leadership group Chiefs for Change, guides administrators step-by-step through the process of designing, implementing, and managing testing in a school district.

  • How can my K-12 school fund a testing program?

     

    The federal government is supporting COVID-19 testing in K-12 schools via the following funding streams:

    Epidemiology and Laboratory Capacity (ELC) Reopening Schools: This money is earmarked specifically to support COVID-19 testing programs in K-12 schools and is flowing through the departments of public health in the US states, territories, and five of the largest cities (New York, Chicago, Los Angeles, Houston, and Philadelphia). For information on how your school can access this funding, contact your state, territorial, or city department of public health.

    Operation Expand Testing (ET): This program, administered by the US Department of Health and Human Services in partnership with the US Department of Defense, has established four coordinating hubs to provide testing for K-8 schools and other “congregate settings” (e.g., homeless shelters and nursing homes) in their respective regions. Schools can contact their regional hubs directly, using the links below.

    • Midwest Hub — Colorado, Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Montana, Nebraska, North Dakota, Ohio, South Dakota, Utah, Wisconsin, Wyoming
    • Northeast and South Hubs — Alabama, Arkansas, Connecticut, Delaware, Florida, Georgia, Kentucky, Louisiana, Maine, Maryland, Massachusetts, Mississippi, New Hampshire, New Jersey, New Mexico, New York, North Carolina, Oklahoma, Pennsylvania, Rhode Island, South Carolina, Tennessee, Texas, Vermont, Virginia, West Virginia
    • West Hub — Alaska, Arizona, California, Hawaii, Idaho, Nevada, Oregon, Pacific Islands, Washington

    Elementary and Secondary School Emergency Relief (ESSER): The US Department of Education has awarded a series of these grants to the state educational agencies in 2020 and 2021. For more information on ESSER funds, contact your state department of education.

    Additional funding options may be available to you at the state or local level, or through private funding entities.

  • What are the reporting and confidentiality requirements for COVID-19 test results?

     

     

    Test results for COVID-19 must be reported to public-health authorities. Reporting requirements can be found on the websites for the US Department of Health and Human Services and the CDC.

    The confidentiality of COVID-19 test results is governed by the Health Insurance Portability and Accountability Act of 1996 (HIPAA). If your organization is a school and is testing students, their test results are also likely to be governed under the Family Educational Rights and Privacy Act (FERPA).

    HIPAA and COVID-19

    Joint Guidance on the Application of FERPA and HIPAA to Student Health Records
     

  • I can’t afford the testing the Calculator recommends. What do I do?

     

     

    First, review the questions and your Calculator inputs to make sure that your responses accurately reflect your current scenario. Misunderstanding a Calculator input could result in more costly recommendations than are necessary.

    Once you’ve determined that the results are accurate, a number of options exist:

    1. Consider how your organization might improve mitigation measures other than testing, such as by emphasizing consistent mask-wearing, incentivizing vaccination among employees, keeping better track of close contacts, or decreasing the size of cohorts that participate in unmasked activity together. Use the Calculator to model various scenarios and predict how improvements in these areas can change your test recommendations.
    2. Seek resources (such as those listed below) to address the cost of a recommended COVID-19 testing protocol. 
    3. If your organization is unable to achieve the levels of mitigation required for safety, consider alternatives to operating in person.

    Federal Support for School COVID-19 Testing — The federal government is supporting COVID-19 testing in K-12 schools via four funding streams. Information and links are available on the Open and Safe Schools website, created by the Shah Family Foundation in partnership with the CDC.

    US Department of Health and Human Services Expanded Testing Coordination Hubs — These four regional hubs aim to provide COVID-19 testing for schools and congregate settings such as nursing homes within their geographic areas.

    Midwest Hub (Colorado, Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Montana, Nebraska, North Dakota, Ohio, South Dakota, Utah, Wisconsin, Wyoming)

    Northeast and South Hubs (Alabama, Arkansas, Connecticut, Delaware, Florida, Georgia, Kentucky, Louisiana, Maine, Maryland, Massachusetts, Mississippi, New Hampshire, New Jersey, New Mexico, New York, North Carolina, Oklahoma, Pennsylvania, Rhode Island, South Carolina, Tennessee, Texas, Vermont, Virginia, West Virginia) 

    West Hub (Alaska, Arizona, California, Hawaii, Idaho, Nevada, Oregon, Pacific Islands, Washington)

  • I understand we need a CLIA waiver to implement most tests on-site. What is a CLIA waiver, and what is involved in obtaining one?

     

    As their website states, “The Centers for Medicare & Medicaid Services (CMS) regulates all laboratory testing (except research) performed on humans in the US through the Clinical Laboratory Improvement Amendments (CLIA). . . . The objective of the CLIA program is to ensure quality laboratory testing.”

    Normally, labs need CLIA certification from CMS in order to perform testing. However, the FDA allows some tests to be performed at labs or other locations that do not have CLIA certification, as long as those sites have a CLIA waiver from CMS.

    CLIA-waived tests tend to have the following characteristics:

    • Simplicity
    • Low risk of user error
    • Conducted using unprocessed samples, such as saliva or nasal secretions
    • Unlikely to harm the patient if the test is not performed correctly

    Your organization can apply for a CLIA waiver via the CMS CLIA website or your local State Agency.

    FDA | CLIA Waiver by Application

    CMS | How to obtain a CLIA Certificate of Waiver

  • What is the difference between isolation and quarantine?

     

    Isolation and quarantine mean essentially the same thing and serve the same purpose: They help protect the public by preventing exposure to people who have or may have a contagious disease.

     

    Isolation separates people who are infected from those who aren’t.

    Quarantine separates people who were exposed to a contagious disease from others and restricts their movements while they wait to see if they are infected.

     

    CDC – When to Quarantine

    CDC – When You Can Be Around Others After You Had or Likely Had COVID-19